The book contains everything you need to play a denizen of the Marches. In addition to rules for ethereal character creation and relevant Resources, the book provides information on ethereal beings, the rules govering them, their domains, and their relations to humans and celestials.

From the back cover:

Once they were gods who ruled the lands of sleep. Once they were spirits who sent their images to slumbering mortals. Once they were elves, unicorns, dragons and more.

The angels tried to kill them. The demons tried to enslave them. But the ethereal spirits survive - and are born anew every night from human dreams! The War may be about Heaven and Hell, but the humans aren't the only ones caught in the crossfire.

Now you can play those mysterious "neutrals," the ethereal spirits - pagan gods, creatures of myth, and even the dancing toothbrushes from the last time you ate anchovies on your pizza. Woven from essential strands of concept, spirits have their own supernatural powers, Song affinities, and personalities.

Play ethereal spirits in their home territories of the Marches... or in the corporeal realm, as they try to regain the glory and worship that was theirs before Uriel's Crusade.